Story highlights

Star Jeremy Renner was like "a ship sitting on the horizon waiting to come in and unload"

Gilroy: There's a much bigger ["Bourne"] world the audience needs to see

The "Bourne" franchise returns to theaters Friday minus its central character, Jason Bourne, but with a new hero and story -- a turn that caught even its writer/director, Tony Gilroy, by surprise.

Gilroy's behind the prior three "Bourne" scripts, and a fourth film wasn't at all in his future plans, the Oscar-nominated director told CNN last week. As for returning for "The Bourne Legacy," Gilroy said, "It wasn't something I anticipated."

In fact, he was initially more akin to the fans who didn't see a need for another "Bourne" film in the first place. "That's where I started," Gilroy said with a laugh. "That's how I came in with that first conversation."

And yet, with all of that hesitancy, the new character he found in Aaron Cross ended up winning him over.

Portrayed by Oscar nominee Jeremy Renner (who's already had a blockbuster summer as Hawkeye in "The Avengers"), Cross is an agent with another government program called Outcome, which creates agents with medically enhanced cognitive and physical capabilities.

Thanks to the actions of Matt Damon's Jason Bourne in the last "Bourne" film, 2007's "The Bourne Ultimatum," Aaron Cross finds himself in jeopardy as Bourne's exposure risk creates problems for Outcome.

The timelines of "The Bourne Ultimatum" and "The Bourne Legacy" are parallel to one another, although you won't see Jason Bourne in this installment.

Neither Damon nor "Ultimatum" director Paul Greengrass were interested in a round four, and "after those guys left, the studio and the estate [of 'Bourne' series author Robert Ludlum] were very aggressively trying to figure out what they were going to do next," Gilroy said. "I don't think I was the only person they were talking to."

They held a meeting, and Gilroy agreed to watch "Ultimatum" for the first time and see whether that sparked any ideas.

Viewing Greengrass' "Ultimatum" made Gilroy ponder what could happen if there was a "larger conspiracy ... and it turns out there's a whole other world outside."

With encouragement from his brother, Dan, who's also a screenwriter and shares credit with Gilroy on "Legacy," Gilroy presented the idea to the studio -- still not expecting that he'd be the one to write the script.

"I came in and thought, hire me for two weeks and I'll play with that idea and we'll figure out who else at the end of it. And it got better than I thought, quickly, and even still it wasn't something that I was going to write, much less direct."

And then, the character of Aaron Cross "came into focus," Gilroy said.

"I realized what a really sort of exciting piece of meat that was to throw on the grill there, and that's when I got more excited and then ... some time after that, I didn't want to let it go. I got into it, and when we made the deal to write the script, why don't we make a directing deal at the same time."

Gilroy's directed two projects before "Legacy," including the well-received George Clooney vehicle "Michael Clayton," but nothing on such a large scale, he said.

"The other films, and I mean this in a good way, they were very claustrophobic. They were very, very contained. Everybody was trapped," Gilroy said. "We're sort of blowing out the walls here and saying there's a much bigger world that the audience needs to see. We expand in specific ways with the camera and how we shoot every day, but also [there's] much more design in this movie. We built a lot more, we travel around the world a lot more, we go a lot wider."

He's also employing a different story structure, having Cross' character converge on the paths of Edward Norton's retired Col. Eric Byer, "the mastermind of the entire franchise," and then Rachel Weisz as Dr. Marta Shearing, a research scientist involved with the Outcome program who teams up with Cross to survive.

Rather than have her enter the plot through Aaron Cross, she's on her own journey, Gilroy said, noting how "that in itself is a really much more open perspective."

Weisz, who told CNN that she's a "huge fan of the original trilogy" as well as writer/director Gilroy, said that what intrigued her about this installment is that "it lifts the curtain on the first three and it shows you who was really in charge, who was really the puppeteer behind all the puppets. So if you think you knew what was happening in the first three, you actually didn't."

The hunt for the right actor to play the franchise's new agent was a long and publicly documented one, a process that was difficult because Gilroy knew he needed an actor with the skill to carry the theatrical components but who could also handle the physical rigor of the shoot.

"The part's really demanding, and Matt [Damon] had established a level of excellence," Gilroy said. "We just needed a really, really great, up-and-down, everyday, can't believe what you're seeing kind of actor. And that person also had to be an athlete ... because of the way these films work, everything's so real. We're not a big green screen, fake-it kind of show."

To top it off, they also needed an actor unknown enough to not draw immediate past references in the minds of moviegoers, but not so new there wasn't any recognition at all. Examining all those needs, the guy left standing was Jeremy Renner.

"Jeremy was just sort of like a ship that was just sitting there right on the horizon waiting to come in and unload," Gilroy said.

For his part, Renner told CNN that while he didn't necessarily feel pressure to live up to Damon, he did hold himself to a personal standard of excellence when it came to performing the action work.

"All I had to really live up to in my mind was that physical part that Matt was doing in the previous films, and that level of authenticity and the ferocity of that action. You can't fake these things," Renner said. "It would do a big disservice to this franchise to not be able to perform what was asked of me and what was required of me."

And as for the skeptics, Gilroy learned to stop worrying about them long ago.

It's known that the "Bourne" franchise hasn't been "the most streamlined 12, 13 years of a franchise; there's been all kinds of rambunctious production history and personality clashes and all the rest of the stuff that's there," Gilroy said. "The one thing that sort of kept it going ... and I think this comes from Matt more than anything else, no one ever really did it for the money. "

The studio might have been driven by dollars, but "everybody was always like, 'if it's not going to be right, we all have other things to do,' " he went on. "So it's like, if there's not a good reason to do it, no one's going to do it. That was true for the first three and that was certainly true for me in this."